Updating posts ready for going live

Posts updated this time:
  - The Eden Project
  - “Da Nang me, Da Nang me. Why Don't They Get a Rope & Hang Me?”
  - A Right Royal Affair
  - The author, slug and categories for every post has also been updated

Also..
 - unsorted the category array for the category_links filter (must have missed that
   when I was copying the code across)
 - added a height to the post-nav class
 - moved post-nav code into a partial include
 - included post-nav partial at the top & bottom of each post type
 - removed unnecessary text at the top of the index page
 - added a disclaimer about the migration process to the index page
 - added a trips.yml data file for storing trip data
 - deleted some unnecessary html page files
 - created category pages for all categories